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Me07 Metals can be arranged due to their voltages

In a previous experiment you have learned: As soon as two aluminium and iron are in contact with a salt solution a voltage can be measured. The surface of your skin is a suitable solution. If you replace these metals by zinc and copper a higher voltage is obtained.
* The voltage between magnesium and copper is 1.22 V
* Middle: Press two different metals between your thumb and fore finger. Use pieces of magnesium, zinc, aluminium, iron, copper.
* Connect these metals with the negative and positive terminals of your multimeter. Write down the voltages. (Change the metals if the meter reads a negative sign.
Observation right: The metals can be put into the following order: Mg < Zn <Al,< Fe < Cu.
Explanation: In the xperiments two metals, the skin and the multimeter work as a Galvanic Cell.
Metals can be put into an order by measuring " Which metals is the better electron donor = produces the higher voltage compared to a positive electrode?"
      (Metals can also be put into an order by comparing their reactions with an acid or with water.
       The order of reactivity will be: Ca>Mg>Al>Zn>Fe>Cu>gold   or. K>Na>Li.